Water jets are commonly used to propel various types of water craft. There are inherent advantages in using water jet propulsion, an important one being that the required water operating depth of a water jet propelled craft can be minimized. This allows the craft to operate in relatively shallow waters or closely to the shore which may be important depending on the uses to which the craft may be put.
Water jets, however, have disadvantages on certain type of vessels. One disadvantage of using water jet propulsion is that air may become entrapped beneath the boat hull and later enters the intake of the water jet. Air entering the water jet propulsion unit results in a loss of thrust and efficiency and tends to overspeed the engine.
This problem is not acute in V-shaped hulls where the presence of aerated water at the apex of the "V" is minimal because of the hull shape. As the inclination of the "V" decreases, however, it becomes more of a problem until when a boat with a flat bottom, sponsons or spaced apart skegs is used, the problem becomes of considerable concern.